1. Field of the Invention
The present invention relates to an information-recording/reproducing apparatus that has a head for recording and reproducing information in and from a recording medium, and a method of detecting the position that the head has with respect to the recording medium in the direction of height.
2. Description of the Related Art
In information-recording/reproducing apparatuses, such as magnetic disk drives, the gap between the head and the recording medium should be as small as possible to meet the demand for high-density recording of information. If the gap is too small, however, the head may contact the recording medium and slide on the medium. If this happens, adverse events will occur, such as errors in recording and/or reproducing information due to the damage to the head and/or the medium, dust making due to the wear of the head and/or medium, and a so-called head crash due to the dust thus made. Thus, the gap between the head and the medium must be reduced, but not so much as to make the head contact the recording medium.
The head is held spaced from the recording medium by a slider that floats from the recording medium because of an air pressure. The distance by which the slider floats from the medium fluctuates in accordance with the process error of the slider, changes in the ambient temperature and changes in the air pressure in the apparatus. To reduce the fluctuation thereby to minimize the gap between the head and the medium, without causing the head to contact the medium, it is proposed that a small actuator utilizing thermal expansion or piezoelectric effect be mounted on the slider to achieve dynamic control of the distance between the head and the medium.
In order to drive the actuator thereby to move the head to an optimal position, the so-called zero-point detection (i.e., detection of the gap between the head and the medium) must be performed. This detection is accomplished by making the head contact the medium once, thereby to determine the position the head has at present. That is, it is determined the distance the actuator is moved until the head contacts the medium, decreasing the distance between the head and medium to zero. Using the point where the head contacts the medium as reference position, the head is then moved away from the medium by a predetermined distance. The head can therefore be held at an appropriate distance from the medium, without the necessity of information about the ambient temperature, the air pressure or the fluctuation of the floating distance of the slider. Here arises a problem with the use of the zero-point detection. Every time the zero-point detection is performed, the head contacts the medium. Consequently, such adverse events as mentioned above may occur in some cases.
To prevent the head from contacting the medium during the zero-point detection, a small AC vibration is applied to the actuator during the zero-point detection, thus shortening the time the head contacts the medium. This method mitigates the adverse events resulting from the head-medium contact. (See, for example, Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2003-308670.)
In the method disclosed in Patent Document 1, however, the head continually contacts the medium many times, not only once. The repeated head-medium contact may sill result in such adverse events as mentioned above.
The actuator may utilize thermal expansion caused by a heater. In this case, a time lag develops during a period between the power-supplying to the heater and the start of the head moving, due to the thermal capacity of the materials of the components ambient to the heater. Inevitably, the head cannot be moved so fast as is described in Patent Document 1. The problem pointed out above cannot be solved.
As is generally known, such hysteresis as shown in FIG. 13 exists as a behavior that is observed when the head contacts the recording medium. That is, once the head contacts the medium as the actuator operates, the head cannot come out of contact with the medium even if it is tried to be moved back to the position it assumes immediately before it contacts the medium. Thus, the slider will not float again unless the head is moved back by a specific distance.
This hysteresis is generally too large to neglect, as compared with the distance the slider floats. If the actuator is operated to move back after the head-medium contact is detected, as is usually done to move the head away from the medium, the head will keep contacting the medium until the hysteresis ceases to exist, as is illustrated in FIG. 13. Inevitably, such adverse events as mentioned above may take place.
In some methods of detecting the head-medium contact, a great amount of data must be processed to determine whether the head has contacted the medium. It may take a long time to determine a head-medium contact in some cases. Then, the head remains in contact with the medium until it is determined that it indeed contacts the medium. In this case, too, such adverse events as mentioned above may take place.